In the operation of tracked machines, wear between the various components comprising a track assembly is a critical concern. Because the machine operates in extremely harsh conditions over all types of terrain, wear of the different components of the track assembly varies drastically.
One type of wear experienced in a track assembly is a phenomenon known as "galling" and has been known to occur, in particular, between the track pin and track bushing that interconnect the sides of the track chain to one another. In a typical track assembly, the track pins are connected to the end portions of a pair of parallel links, while the track bushings are connected to the opposite, but overlapping end portions of the parallel links. The track pins are received within a bore defined by the track bushings and the two components rotate relative to one another as the driven track chain rotates around the sprocket and idlers of the track assembly. In an attempt to control wear, a clearance is provided between the track pin and bushing in which lubricating fluid may reside that is contained in a reservoir defined by the track pin. As the track pin and bushing oscillate with respect to one another, the lubricant is intended to cover the interface between the two components and greatly reduce the "galling" that would otherwise occur therebetween.
The problem that exists, particularly in the track chains of extremely large machines, is the distribution, or lack thereof, of the lubricant to the area of interface between the track pin and bushing. Typically, the oscillation angle between the track pin and bushing is relatively small, generally about 30 degrees. The track pin and the bore of the bushing, in which the track pin resides, are known to be cylindrical in configuration. The diameter of the pin and the diameter of the bore are very nearly the same with the bore being slightly larger to provide a slight clearance therebetween for the lubricant. The load applied to the pin and bushing is distributed along the area of interface, or oscillation, and, unless the clearance is relatively large, this interface may never separate enough to be lubricated by the fluid present in the clearance. In these instances, the effect of the lubricant is minimal and galling will occur resulting in premature wear.
One solution to this situation is to increase the size of the clearance between the track pin the bore of the bushing to reduce the area of load distribution. This has been known to improve the galling between the pin and the bushing by allowing the flow of lubricant to the area of interface. The sealing arrangement, however, positioned between the track links and the track bushing to maintain the reservoir of lubricant within the track pin and the clearance is taxed. With an increase in clearance, the amount of relative movement between the track pin and bushing is also increased. The seal assemblies must accommodate this increase in relative movement and the amount of allowable increase in clearance is greatly limited by typical sealing systems. This has been known to cause premature failure of the track joint.
The present invention is directed to overcoming one or more of the problems as set forth above.